Gaseous discharge circuit



Oct. 16, 1951 M. R. BOYD ETAL GASEOUS DISCHARGE CIRCUIT Filed Aug. 25,.1949

A A A A ll JIZUGIZZ'OrS:

M44004, A. Bow, AND

Patented Oct. 16, 1951 GASEOUS DISCHARGE CIRCUIT Malcolm E. Boyd, Hightstown, and Louis Malter,

Princeton, N. J., assignors to Radio Corporation of America, a corporation of Delaware Application August 25, 1949, Serial No. 112,211

14 Claims.

In electrical circuit arrangements, it is oftentimes desirable to provide self-excited oscillators or multivibrators of a type which may be easily synchronized. In the interest of simplicity andeconomy and where operating conditions permit, it is often convenient to utilize the wellknown form of gaseous discharge tube commonly termed Thyratron. The basic elements of this tube are substantially the same as a triode vacuum tube. However, inasmuch as the elements are incorporated in an atmosphere of gas, the operating characteristics of the Thyratron are entirely different from vacuum triode types. In

most respects, the Thyratron or controllable discharge tube characteristics, being of a virtually on or off nature, makes it eminently suited for such relaxation oscillator or multivibrator application. However, it is well recognized that due to the required de-ionization time of the gas in the Thyratron envelope, upon cessation of active excitation, the operating frequency limit of oscillators using Thyratron is severely limited.

This limitation is perhaps more severely felt in the television field wherein the interests of efficiency, it would be highly desirable to base horizontal electromagnetic deflection circuits solely on Thyratrons. The inherent low voltage drop across such gas tubes, as well as their relatively large peak current carrying capacities, make them ideally suited for such applications provided stable operation could be achieved at the higher frequencies required. It is because of this instability due to gas deionization time that Thyratron circuits have not been commonly employed for such deflection circuit applications.

It is therefore an object of the present invention to provide an improved form of oscillator circuit utilizing controllable gaseous discharge tubes.

It is another object of the present invention to provide a new and improved form of electromagnetic cathode ray beam deflection circuit particularly suited for television application in which the gaseous discharge tube or Thyratron is employed as the deflection output device.

It is a further object of the present invention to provide a novel form of control circuit for use with multi-electrode gaseous discharge tubes such that their application in oscillatory circuits is made more valuable due to an increase of the frequency ilmit normally imposed by gas deionization time.

In the realization of the above objects, the present invention in its more general form contemplates the use of a control voltage developing circuit which is synchronously operated in accordance with the oscillator action of the circuit involving the gaseous discharge tube. The output voltage of the control circuit is so polarized to cyclically drive the control electrode of the discharge tube highly negative relative to the discharge tube cathode for a suitable interval prior to the application of synchronizing firing stimulus to the discharge tube. The highly negative swing allows the control electrode of the discharge tube to regain control of the discharge path more quickly than in prior art systems thereby enhancing the effective recovery time of a gas tube to a degree permitting more stable operation of the oscillator circuit and its possible accuracy of synchronization.

In one of its more limited aspects, the present invention contemplates the use of a gaseous discharge tube in a horizontal deflection circuit for a television receiver. A suitable control signal transformer having a primary-to-secondary is connected in the output and input circuits of the gaseous deflection output tube with such polarity that required voltage variations in the output circuit produce highly negative-going pulses in the control circuit of the discharge tube and thereby provide more stable and more easily controllable deflection Waveform generation.

Other objects and features of advantages in addition to those set forth hereinabove and hereinafter, as well as a more complete understanding of the mode of operation of the present invention will follow perusal of the following specification, especially when taken in connection with the accompanying drawing in which:

Figure 1 illustrates a form of synchronizable gaseous discharge oscillator eminently suited for application as an electromagnetic deflection generator in television receivers;

Figure 2 shows various operating waveforms peculiar to the operation of the embodiment of the present invention as illustrated in Figure 1.

In order to more fully understand the novel mode of operation of the present invention, as well as the many distinct benefits to be derived therefrom, reference is now made to Figure 1 in 3 which there is shown a gaseous discharge tube H] of the Thyratron variety adapted for excitation of a typical television electromagnetic deflection yoke I2. Positive biasing potential for the anode I4 of the discharge tube I!) is then supplied from the positive biasingsupply terminal It through the primary winding 18 of a cone trol transformer 28. The secondary winding 22,

32, in series combination with the parallel RC; network comprising resistance 3-4 and capacitor 38, is placed in shunt with the yoke winding. Periodically recurrent sync signal 38 is then applied through capacitor 48 to the control grid 28 of the discharge tube with positive-going polarity to effect firing and synchronization of the deflection circuit.

In considerin the operation of the deflection circuit and for convenience in labeling the curves in Figure 2, the gaseous discharge tube It will be designated as V1, diode 32 designated as V2, the inductance of the deflection 12 designated as Ld, the inductance of the transformer primary I8 as L1, and the inductance of the transformer secondary 22 as L2.

Inasmuch as the description of the operation of any oscillatory circuit" demands the initial assumption of some arbitrary static condition, it shall be assumed that the capacitor 28 has been allowed to fully charge from the power supply terminal l6 through the inductance L1, and gas tube V1 is in a quiescent condition. The arrival of positive-going sync pulse 38 will then cause discharge tube V1 to fire and the potential of the anode l4 thereof will immediately drop to a potential only several volts above ground. This firing may be thought of as occurring at the time in Figure 2 where it will be noted in curve 2d that the voltage VPV has dropped to a low value of several volts. Upon firing of tube V1 a current will then start to flow through the yoke inductance La due to the then charged condition of capacitor 28. This current flow behaves sinusoidally, being based upon the resonant frequency of the yoke inductance Lu and the capacitor 28. After one-quarter cycle of a sinusoidal current flow, the voltage across the capacitor 28 will then reverse causing the cathode of the diode V2 to become negative with respect to its associated anode. automatically and the voltage across inductance Ld is held substantially constant durin the ensuing sweep interval t1-t2 or Ts. The constant voltage so produced across the yoke inductance lid is a function of the time constant of the RC circuit comprising elements 34 and 36 and of the characteristics of the damping tube in accordance with well-known deflection circuit damping principles. Furthermore, with a substantially constant voltage across the inductance La, the current in through the yoke I2 will then begin to rise linearly as shown in curve 20 to form the linear rise portion of the required sawtooth deflection current.

The energy stored in inductance Ld then, taking the form of current fiow, is dissipated through Diode V2 then fires the diode V2, resistance 34 and partially stored in capacitor 36. The capacitor 36 is large and acts to hold the voltage constant during the deflection interval Ts while the resistance 34 dissipates the power initially stored in the inductance La. tioned such that the current through the diode V2 becomes substantially 'zero at or immediately following the end of the sweep interval Ts.-

will however continue to be a small current'flow through the tube from some time after the initiation of the sweep interval Ts.

It will beseen, however, that upon further extinction of the discharge tube V1, the capacitor 28 will then begin to charge through the primary 18 of the control transformer 28, As it charges through the inductance L1, the current waveform will be substantially sinusoidal and the voltage appearing across the primary I8 (L1) will be substantially that shown by :curve 2w.

If now, according to the present invention,=the

secondary .22 of the control transformer 28 "is properlyv poled with respect to the primary 18 so that the secondary voltage across L2 is out of phase with respect to the primary v'oltage across L1, the control voltage applied to the control electrode 26 will be substantially that shown by curve 21). By inspecting the voltage variation on the anode of the discharge tube 10, as shown .in curve 2d,'inrelation to the voltage applied to the control electrode '26, as shown; in

curve 21), it will be seen that as the potential on the anode I of the discharge tube H) increases (curve 2d), the control electrode voltage (curve 2b) swings highly negative thereby tending to discourage refiring of the discharge tube due-to any residual gas ionization in the tube envelope.

Furthermore, this negative-going controlvoltage will provide a degree of noise immunity against incoming positive-going signals other than sync.

Thus, the noise immunity of the circuit against mis-synchronization by unwanted noise signals during the deflection cycle Ts is greatly enhanced while the high negative voltage applied to the control electrode greatly decreases the effective grid recover time of the discharge tube.

In general, the inductance L1 and the capacitor 28 are so chosen that approximatelyone-half wave is completed during the interval Ts. This waveform must have as its A. C. axis the value of the D. C. input voltage appearing at the power supply terminal [6. The voltage across capacitor 28 therefore swings as far above this axis as it does below so that the capacitor 28 acquires a peak voltage approximately twice that of the power supply. Inductance L1 and capacitor 28 may be so chosen that more than one-half cycle remain low thus allowing further time for deionization of the Thyratron. i

It will be apparent from the above that the utility .of the present invention is in no way limited to the specific transformer arrangement shown nor to the utilization of a gaseous diode in the position of V2. V2 may, under certain con- Resistance. 34 generally proporditions, b'e'repla'cedby a vacuum diode if desired while other methods may be employed to derive the negative-going control signal for the control electrode of the discharge tube in accordance with electrical variations in the discharge tube output circuit. 7

In the practice of the present invention, it may be desired to adjust the turns ratio of the transformer 20 to be approximately equal to the ratio of the D. C. voltage appearing at the positive power supply terminal Eb to the biasing voltage Ec appearing at terminal 24. This allows maximumswing to be obtained without driving the-control electrode 26 positive during the early part of the deflection cycle.

We claim:

1. In an electrical circuit the combination comprising a gaseous discharge tube having at least an anode, a cathode and control electrode, an output circuit connected between the anode and cathode of said discharge tube, an input circuit connected between the control electrode and cathode of said discharge tube, an inductive element connected in the output circuit of said discharge tube, a unilaterally conductive damping circuit connected in shunt with said inductive element, means for applying timing pulses to the input circuit of said discharge tube for effecting periodic control thereof, means responsive to output circuit current variations upon conduction of said discharge tube to develop a control signal having positive and negative extremities, and means for applying said control signal to the control electrode of said discharge tube such that the negative extremity of said control signal is active to swing said control grid negatively with respect to the cathode of said discharge tube just prior to conduction of said discharge tube.

2. Apparatus according to claim 1 wherein said unilaterally conductive damping circuit comprises a diode having an anode and cathode in series with a parallel resistance-capacity network.

3. Apparatus according to claim 2 wherein said unilaterally conductive damping circuit diode is a gaseous discharge tube.

4. In an electrical circuit, the combination of, a gaseous discharge tube having an anode, a cathode, and control electrode, an output circuit connected between the anode and cathode of said discharge tube, an input circuit connected between the control electrode and cathode of said discharge tube, a transformer having a primary and secondary, an inductive element connected in series with said transformer primary to form a combination, connections placing said combination in said discharge tube output circuit, a unilaterally conductive damping path in shunt with said inductance, means for applying periodically recurrent timing pulses to said input circuit in such polarity to swing said discharge tube control electrode in a positive direction with respect to said cathode, and connections placing said transformer secondary in the input circuit of said discharge tube, the phasing of said transformer secondary relative to said transformer primary being such that said control electrode is swung negatively with respect to said cathode just prior to conduction of said discharge tube.

5. Apparatus according to claim 4 wherein a unidirectional anode biasing polarizing potential of E1 is imposed in series with said output circuit and a control electrode biasing potential of -E2 is imposed in series with said input circuit,

and wherein the primary to secondary turns ratio of said transformer is approximately equal 6. Apparatus according to claim 5,wherein a capacitor is placed in shunt with the primary of said transformer to form a resonant circuit Whose resonant frequency is approximately equal to the periodic recurrence of said timing pulses. 7. Apparatus according to claim 5 wherein said unilaterally conductive damping path comprises a .gaseous discharge diode connected in series with a resistance-capacity time constant circuit.

8. An electromagnetic deflection generator for a cathode ray deflection system employing a deflection yoke having an input winding, said circuit comprising in combination, a gaseous discharge tube having an anode, cathode and control electrode, a positive power supply terminal, an output circuit including said discharge tube anode, said positive power supply terminal and said discharge tube cathode, connections placing the deflection yoke input winding in series with said output circuit, a unilaterally conductive damping circuit connected in shunt with said deflection yoke input Winding, an input circuit connected between said discharge tube control electrode and cathode, means for applying periodically recurrent timing pulses to said input circuit in such polarity to fire said gaseous discharge tube, means connected with said output circuit responsive to electrical variations in said output circuit following firing of said discharge tube to derive an alternating current control signal, and means for applying said control signal to said input circuit with such polarity and amplitude to swing said control electrode negatively with respect to said discharge tube cathode for disabling thereof.

9. Apparatus according to claim 8 wherein said unilaterally conductive damping circuit comprises a diode serially connected with a parallel resistance-capacity network.

10. Apparatus according to claim 9 wherein said damping circuit diode is of the gaseous discharge variety.

11. An electromagnetic deflection generator for a, cathode ray system employing a deflection yoke having an input winding, said circuit comprising in combination, a gaseous discharge tube having an anode, cathode and control electrode, a positive power supply terminal, an output circuit including said discharge tube anode, said positive power supply terminal, and discharge tube cathode, connections placing the deflection yoke input winding in series with said output circuit, a unilaterally conductive damping circuit connected in shunt with said deflection yoke input winding, an input circuit connected between said discharge tube control electrode and cathode, means for applying periodically recurrent timing pulses to said input circuit in such polarity to fire said gaseous discharge tube, a transformer having a primary and secondary winding, connections placing the primary and secondary of said transformer respectively in series with the output and input circuits of said discharge tube, the phasing of said transformer secondary relative to its primary being such to swing said discharge tube control electrode highly negative relative to its cathode subsequent to firing of said discharge tube.

charge tube and wherein said transformer pri- -mary is connected between said positivepower supply terminal and the other terminal of said deflection yoke input winding.

7 14. Apparatus according to claim 13. wherein said input circuit incorporates a source of negative biasing potential for said discharge tube-control electrode and wherein the --primar.y-'tosecondary turns ratio of said'transformer is equal to the numerical ratio of said'positive power supply terminal potential to said negative control electrode biasing potential. v

- MALCOLM R. BOYD.

LOUIS MALTER'.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 15 2,217,831 Ballard Oct. 15,1940

Andrieu ;Dec; 16,3941 

